The illusion of catch-up growth in premature infants. Use of the growth index and age correction
W. Karniski, C. Blair and J. S. Vitucci
Growth data of 61 premature infants who were observed for 29 months were
analyzed to determine if there is validity to the concept of catch-up
growth. Weight, length, and head circumference were recorded at each visit.
For each measurement, a growth index was calculated to facilitate
comparison of infants of different ages and sexes. The age of a child at
each visit was also corrected for prematurity by subtracting the number of
weeks premature from the postnatal chronological age to generate a
corrected age. The corrected age was then used to create a corrected growth
index for all variables at each visit. Growth data evaluated in the
traditional manner (without correction) suggested that catch-up growth
occurred. However, growth data for corrected age more closely approximated
the growth of full-term children. Graphic impressions were generally
substantiated by Hotelling's T2 tests and factorial and one-way
repeated-measures analyses of variance with Bonferroni adjustments. The
corrected growth data of appropriate-for-gestational-age children
approximated normal expected growth, whereas small-for-gestational-age
children still demonstrated subnormal growth at 29 months of age, despite
correction. In both appropriate-for-gestational-age and
small-for-gestational-age children, catch-up growth appears to be a
statistical illusion created by charting growth of premature infants using
chronological age rather than the more appropriate corrected age. This
finding has important implications for the follow-up of premature infants
and may affect the diagnostic interpretation of failure to thrive.
